For LBBB, Smith et al. derived and validated a "modified Sgarbossa rule" in which they replaced Sgarbossa's third criterion (excessively discordant ST elevation as defined by 5 mm) with a proportion-based criterion (defined by > 25% of the previous S-wave) (see Table 1). This rule resulted in much higher sensitivity and accuracy for diagnosis of ACO than the original Sgarbossa.7,8